1. Field of the Invention
This invention relates to a metering device suitable for a photographic camera, and more particularly to a metering device which meters an object field by dividing it into a plurality of areas and produces a proper metering output for imparting a proper exposure to the entire photographing picture plane on the basis of metering outputs corresponding to the plurality of areas.
2. Description of the Prior Art
Difficult problems in metering an object field lie in judging the position at which a subject intended by the photographed exists with respect to the object field which can be expressed by the distribution of luminance, and determining the exposure value necessary to photograph the subject. For example, as an exposure determining system for solving the above-noted problems, there is a center priority metering system. This is a system whereby the brightness of the central portion of an object to be photographed is metered and the exposure amount is determined on the basis of the metered value. However, when this metering system is resorted to, no proper exposure can be obtained where the subject does not exist in the central portion of the picture plane. It often occurs that the subject of photography exists in the marginal portion of the picture plane and therefore, the conventional center priority metering system has a disadvantage in that the probability with which a proper exposure is obtained is low.
Japanese Patent Publication No. 33794/1972 discloses a metering system whereby the entire object field which is the object of metering is divided into suitable small areas and a geometrical mean value, a maximum value, a minimum value, contrast, an arithmetical mean value, etc. are obtained from the metered values of the areas.
This metering system is very excellent as a method of obtaining metering data which provide the basis for judgment for obtaining a desired exposure amount of object fields of various luminance distributions or for photography directed to various purposes. However, it is not easy to judge what exposure amount should actually be imparted on the basis of the obtained metering data.
Further related examples of the prior art include Japanese Patent Publication No. 9271/1976 which discloses a technique in which the arithmetical mean value of the maximum value and the minimum value of a plurality of metering outputs is used as a proper metering output, and Japanese Laid-open Patent Application No. 17725/1978 which discloses a technique in which the intermediate value of the maximum value and the minimum value is manually extracted by the photographer and this intermediate value is used as a proper metering output.
However, these prior arts have the following disadvantages. That is, in a case where the exposure is determined by the arithmetical mean value, the major object sometimes becomes under-exposed or over-exposed under special object field conditions such as counter-light conditions or conditions in which the major object lies on the snow. Also, setting the intermediate value so as to be a proper exposure under the above-mentioned special object field conditions not only requires skill, but also unavoidably involves the reduction of operability because the setting operation is manual.